1. Field of the Invention
The present invention relates to a bipolar voltage controlled optical switch for single-mode light using two intersecting waveguides.
2. Description of the Prior Art
An optical switch is a switching circuit which enables signals in optical waveguides to be selectively switched from one path to another by using electro-optic effects.
Known optical switches include total-internal-reflection (TIR)-type optical switches and directional-coupler-type optical switches. TIR-type optical switches are attractive because of their simple structure and mechanism, but have the disadvantage of poor crosstalk characteristics and a high operating voltage for single-mode light. Note that most of the TIR-type switches have been used for multi-mode light. In this case, although these switches have a relatively low operating voltage, the switches have high excitation dependency.
Directional-coupler-type optical switches usually have two separate waveguides. In these switches, asymmetric changes are electrically induced in the refractive indexes of the waveguides so as to switch signals in the waveguides from one path to another or vice versa. However, these switches are so complex in structure due to the presence of a gap between the waveguides that fabrication errors are often generated. For improving this, a .DELTA..beta.-reversal type directional-coupler switch has been proposed, however, it requires complex electrodes.
On the other hand, a directional-coupler-type optical switch with no gap between waveguides, i.e., with intersecting waveguides, has been proposed (See: M. Papuchon and Am. Roy, "Electrically Active Optical Bifurcation: BOA", Applied Physics Letters, Vol. 31, No. 4, Aug. 15, 1977). This optical switch comprises a central waveguide, a pair of input waveguides connected to an end of the central waveguide, and a pair of output waveguides connected to the other end of the central waveguide. In this switch, the entire central waveguide is a refractive-index-changed region. As will be explained later, such as BOA switch requires high refractive index change, so that a relatively high operating voltage is also required. As a result, the switching speed is decreased.